1. Field of the Invention
The present invention relates to a cuff of a wrist-mount blood pressure monitor which is used in a blood pressure monitor which is mounted on the body of a subject so as to measure blood pressure and, more particularly, to a structure of the cuff of a wrist-mount blood pressure monitor used in a wrist-mount blood pressure monitor for monitoring the blood pressure on the wrist.
2. Description of the Related Art
In general, the cuff of the wrist-mount blood pressure monitor to be used in a wrist-mount blood pressure monitor is composed of an inflatable bag into which a fluid such as air is supplied, and a fixing member to be mounted on a portion of a subject. After the inflatable bag is mounted on the wrist by using the fixing member, gas such as air is supplied to the inflatable bag, so that the artery of the subject is pressed and blood pressure is measured at a pressuring process or an exhaust process of the inflatable bag. As the fixing member, a band type cuff band, a holding elastic plate disclosed in Japanese Patent Application Laid-Open No. 9-224916 (1997) or the like can be used.
In the prior cuff of the wrist-mount blood pressure monitor having the above structure, however, since the fixing member is composed of a member with elasticity from a viewpoint of facilitation or the like of the mounting on the wrist, there arises a problem that the fixing member stretches and is deformed according to expansion of the inflatable bag. This problem will be explained with reference to FIGS. 10A and 10B.
FIGS. 10A and 10B are diagrams showing a cross section of a wrist, and FIG. 10A shows a state before the inflatable bag 51 is inflated, and FIG. 10B shows a state where the inflatable bag 51 is inflated. As shown in FIG. 10A, the cuff of the wrist-mount blood pressure monitor 50, which is composed of the inflatable bag 51 and a band-type cuff band 52 as the fixing member, is wound around the wrist 101. As shown in FIG. 10B, the inflatable bag 51 is then inflated, so that radial artery 104 in a vicinity of a radius 102 and ulnar artery 105 in a vicinity of an ulna 103 are pressed.
Since the cuff band 52 is, however, composed of the member with elasticity, the inflatable bag 51 inflates to the side of the wrist 101, and the cuff band 52 stretches and deforms so that the inflatable bag 51 inflates greatly to a direction separating from the wrist 101. At this time, as shown in FIGS. 10A and 10B, a distance (d1) from the radius 102 to the cuff band 52 increases. That the distance (d1) is large means that it is necessary to largely inflate the inflatable bag 51 in order to press the wrist 101. For this reason, a flow rate of an air pump for inflating the inflatable bag 51 should be increased, and thus it is difficult to miniaturize the air pump.
Although a tension is generated in the inflatable bag 51 according to its expansion, as the inflatable bag 51 inflates more largely, the tension to be generated becomes stronger, thus deteriorating efficiency of pressure transmission to a blood vessel wall to be pressed. A phenomenon such that the pressure to be transmitted to the blood vessel wall to be pressed (blood pressure of blood vessel inner wall to be pressed) is stronger than internal pressure in the air bag, therefore, occurs, and thus there also arises a problem that the blood pressure cannot be measured properly.
The measuring principle of an oscillometric method is established under the presumption that the pressure of the blood vessel inner wall to be pressed is equal with the pressure in the inflatable bag, and thus the pressure of the blood vessel inner wall to be pressed is estimated to be the pressure in he pressing fluid bag. For this reason, when the pressing force of the blood vessel to be pressed becomes insufficient, the pressure in the inflatable bag becomes higher than the pressure of the blood vessel inner wall to be pressed at the time when the blood vessel to be pressed is broken, and the blood pressure is measured high.
As the fixing member, there are a method of winding an elastic plate harder than the cuff band around the wrist and a method of connecting a plurality of curved covers via hinges and winding them around the wrist. Since they, however, use an elastic member as a material or a fastening method, the above-mentioned problems arise.